Various communication systems communicate using multiple transmit and/or receive antennas. Such communication schemes are referred to as Multiple-Input Multiple-Output (MIMO) schemes. MIMO configurations are used, for example, in Evolved Universal Terrestrial Radio Access (E-UTRA), also referred to as Long Term Evolution (LTE), and LTE-Advanced (LTE-A) systems. MIMO communication typically involves feeding back communication channel information from the receiver to the transmitter.
Various techniques for calculating and transmitting channel feedback are known in the art. For example, feedback schemes that are based on reciprocity between uplink and downlink channel are described in document R1-094443 of the Third generation Partnership Project (3GPP) Technical Specification Group (TSG) Radio Access Network (RAN), entitled “On Channel Reciprocity for Enhanced DL Multi-Antenna Transmission,” Jeju, Korea, Nov. 9-13, 2009, which is incorporated herein by reference in its entirety. As another example, 3GPP TSG RAN document R1-094690, entitled “Use of UL Covariance for Downlink MIMO in FDD,” Jeju, Korea, Nov. 9-13, 2009, which is incorporated herein by reference in its entirety, discusses the use of the uplink covariance matrix for downlink MIMO.
Some MIMO feedback schemes use precoding codebooks, i.e., predefined sets of precoding matrices. Codebook-based feedback schemes are described, for example, in 3GPP Technical Specification 36.213, entitled “Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer Procedures (Release 8),” (3GPP TS 36.213), version 8.6.0, March, 2009, which is incorporated herein by reference in its entirety. Other codebook-based schemes are described in 3GPP TSG RAN document R1-94686, entitled “Codebook for 8Tx DL SU-MIMO for LTE-A,” Jeju, Korea, Nov. 9-13, 2009, which is incorporated herein by reference in its entirety. Yet another example scheme is described in 3GPP TSG RAN document R1-903888, entitled “Precoding Options for 8Tx Antennas in LTE-A DL,” Ljubljana, Slovenia, Jan. 12-16, 2009, which is incorporated herein by reference in its entirety.
Some MIMO feedback schemes are defined for cross-polarized antenna arrays. An example technique of this kind is described in 3GPP TSG RAN document R1-94844, entitled “Low Overhead Feedback of Spatial Covariance Matrix,” Jeju, Korea, Nov. 9-13, 2009, which is incorporated herein by reference in its entirety. Another example is described in 3GPP TSG RAN document R1-91229, entitled “Discussion on Enhanced DL Beamforming,” Seoul, Korea, Mar. 23-27, 2009, which is incorporated herein by reference in its entirety.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.